Twitch API changes have broken this extension, for most users. You can view video but, login is failing (so no chat or user presence.) Until it's updated, you'll need to find another method. This is by far the best Twitch viewing experience, when it works. I'd donate in a heartbeat if the creator relocated and started taking other currencies ...
If you have browser extension DuckDuckGo Privacy Essentials (or similar privacy extensions) installed, try to disable/remove it. Also read the built-in help in the player.
